Technical Abstract:
Compositions of minor constituents in vegetable oils affect oil properties, quality, and stability. The applicability of capillary electrochromatography (CEC) photodiode array detection for the simultaneous separation and quantification of the oil chemical compositions was explored. Since we have done extensive high performance liquid chromatographic (HPLC) studies on the minor oil constituents tocopherols (T), tocotrienols (T3), and phospholipids, the results of the present study are compared with those of HPLC. In the CEC system, a capillary column (25 cm x 100 um I.D.) packed with 3-um porous C8 bonded silica was used, while voltage, temperature, and electrokinetic injection settings were maintained at 25 kV, 30 deg C, and 10 kV/10s, respectively. The detector was set at 290 nm for tocopherols/tocotrienols and 200 nm for phospholipids. The vitamin E active compounds (lipid antioxidants) were separated with a mobile phase of acetonitrile 25 mM TRIS (95:5). Under these conditions, a base line separation of a 10 component mixture was obtained with elution order similar to that observed in reversed phase HPLC: delta T3>(gamma+beta)T3>alphaT3>epsilonT> deltaT>(gamma+beta)T>alphaT>alphaT- acetate CEC of the antioxidant acetates yielded less satisfactory results. Effects of CEC experimental variables (e.g. mobile phase solvents and buffers, stationary phases, and electric field) on analyte separations were evaluated. Applications to vegetable oil analyses are described. Preliminary results from CEC separations of selected phospholipids classes and molecular species are presented.